Wanted: Propulsion engineers

[Tollytime]

As you all may know, I'm a noob and I'm trying to break into this hobby.My second project happens to be a complete custom build. I am aware it's not the most intelligent way to embrace this hobby. I'm interested in getting my propulsion setup before I go any further on the Enterprise tug project. I really don't know much of anything in this category at all. This may be quite a tall order, but here it goes. I have a list of what I got and another list of questions to be answered. I won't blame anybody for shaking their head and clicking to the next thread.

1. A 6volt 9.5 ah battery (Power Wheels)

2. 1/8" drive shaft that's 14 3/8" long with 3/16" thread adapter.

3. 1/4" stuffing tube with oilite bearings already installed in hull (can not remove).

4. 6 volt 10,000 rpm Dumas motor (The cheaper 540, not a 5,000rpm) with Dumas coupling.

5. Pro Boat 6volt ESC (Waterproof).

6. 2" four bladed prop with 3/16" thread.

7. A SubTech 1/8" shaft seal for 1/4 stuffing tube.

8. The hull with battery and ballast weighs at least over 20lbs.

Bear with me, here are my questions:

1. Can anyone suggest a reduction gear? What make would you use?

2. Should I spring the cash for the more powerful Dumas 6volt motor or can you make a better suggestion?

3. The top of my stuffing tube is below the waterline, should I install the SubTech 1/8" shaft seal on the end of my stuffing tube? Would the oilite bearings and some Super Lube be enough to prevent leaking?

4. I see fancy shaft collars on drive shafts. I really have no clue on what you setup on the drive shaft with the prop.

I could really use some input.

Thank you for your time

[patmat2350]

T'time:
Before you go ANY further- put a strut or brace on the end of that tube. Any unbalance (unavoidable, think about weeds) will cause that free unsupported brass tube to flail around, that's a bad thing. If you can move it with a finger tip, bad.

I'll get back unless someone else beats me to it with some more ideas, got to go to work now!

Pat M

[patmat2350]

Tolly- OK, they changed my start time, got more time!

1. Toss the 1/8 shaft and seal, get a 3/16" stainless shaft (unless you like silver soldering and have access to a lathe). Prefer precision ground shafting from someone like sdp-si.com or mcmaster.com... nonprecision stuff may need to be worked down with emery cloth for free running.
Prefer a lathe for this, but can use soft jaws in a vise... grab the shaft and run 10-32 threads on the end with a die and handle, that will fit your prop. If any doubt about the prop's threads, try it with screws from the hardware store.

2. Also get a 10-32 locknut and a close fitting washer to act as a cheap thrust washer.

3. Really, brace the end of that tube.

4. I assume 1/4 OD on the tube? Your best bet is to sleeve it with a piece of 7/32 brass tube to act as a bearing for the 3/16" shaft. CA can hold it in place.

5. Get a 2.5:1 or 3:1 reduction gear from Master Airscrew http://www.masterairscrew.com/GoCart/itemlist.asp?ID=1265&RootID=1056
I think you can also get a nice mounting bracket from them.
Remove the prop adaptor, and you have a 3/16" output shaft...

6. Which is perfect to couple to your 3/16 prop shaft with a Dumas dogbone coupler, available from Dumas or most hobby shops.

7. Alternative: Direct drive with a very inexpensive 550 motor from Vac-u-Boat www.vac-u-boat.com. Might be too slow on 6v. They also have nice couplers, equivalent to the Dumas dogbone.

Always good to leave the mounting area flexible in order to try different drive set ups!

Pat M
who has several pieces in "Ships in Scale" www.seaways.com on gearboxes and couplers and such (shameless plug...)

p.s.: Not in Propulsion as such, but I AM a driveline engineer :cool:

[patmat2350]

But wait there's more!

You mentioned collars... You can get a cheap 3/16 ID collar from the hobby shop, look in the model plane parts. You can use this on the upper end with another thrust washer, setting the shaft's free play to about 1/32 or less. Keep in mind that this end takes the thrust load when in reverse.

Then you can extend the shaft a bit if necessary to reach the dogbone coupler and motor. If the reach is too long, don't cantilever the shaft; cut the nylon dogbone in two, and extend its length with a piece of 7/32 OD iirc aluminum tube. Micro screws can pin tube to nylon, don't count on glue.

Pat M

[Tollytime]

T'time:
Before you go ANY further- put a strut or brace on the end of that tube. Any unbalance (unavoidable, think about weeds) will cause that free unsupported brass tube to flail around, that's a bad thing. If you can move it with a finger tip, bad.

I'll get back unless someone else beats me to it with some more ideas, got to go to work now!

Pat M
A vertical strut will be installed, I knew you would point that out. Not to mention the vibration of pushing a 20lb+ boat with a 2" prop. I got some really bad news about the shaft. I figured out earlier I really needed a 3/16" shaft but its too late, or at least I think it is. The Dumas Osprey instructions called for installing an oilite bearing in the center of the stuffing tube for the 1/8" shaft before you build the hull. I could try to put De-bonder in the tube and knock it out, but I'm afraid of bending the stuffing tube. I really don't want to try to remove the shaft at this point either. The rest sounds good though.

[patmat2350]

Never say never.
The Oilite bearing is not likely well bonded to the tube. Put a 3/16 shaft in there and tap it lightly, I won't be surprised if the bushing moves out quite easily... dribble in the debonder first if you like.
If you must stay with the 1/8 shaft- I'd be happy to put a 3/16" stub on there, trued in a lathe...

Pat M

[Tollytime]

Never say never.
The Oilite bearing is not likely well bonded to the tube. Put a 3/16 shaft in there and tap it lightly, I won't be surprised if the bushing moves out quite easily... dribble in the debonder first if you like.
If you must stay with the 1/8 shaft- I'd be happy to put a 3/16" stub on there, trued in a lathe...

Pat M
I'll give it a try, but theres a good amount of C/A in there. I've got Ships n Things building me a custom 1/8 shaft with a 3/16 thread on the end. I screwed up on the measurements and had to send it back. I expect it soon.